Method of making 4-nitrotoluene



Sept. 15, 1964 L. u. BERMAN ETAL 3,

METHOD OF MAKING 4-NITROTOLUENE Filed April 25, 1962 CE LLULOSE N ITRAT E ADD MERCURY OR MERCURY SALT CATALYST ADD RELATWELY D\LUTE AQUEOUS HNO LHEAT (2o- 85C) I E I'II L SEPARATE om: souos I SOUDS I LlQUlD T I RECYC LE I SEPARATE INVENTORS LAWRENCE u. BERMAN RVZHARD H. c ousE BY V United States Patent 3,149,169 METHQD 9F MAKING 4-NKTRGTOLUENE Lawrence U. Herman, Slrolrie, and Richard H. Crouse,

La Grange Park, IlL, assignors, by mesne assignments,

to Union Carbide Corporation, New York, N31, a

corporation of New Yorlr Filed Apr. 23, 1962, Ser. No. 189,327 Claims. (Cl. 260-645) The present invention relates to a method of producing 4-nitrotoluene in relatively large yields and more particularly relatesto a method for the selective nitration of toluene to readily produce the paraisomer thereof which method includes the treatment of toluene with cellulose nitrate and relatively dilute nitric acid in the presence of a catalyst as hereinafter set forth.

At the present time nitrated toluenes are standardly prepared by a so-called mixed acid process which involves the nitration of the hydrocarbon material in the presence of a mixture of concentrated sulphuric and nitric acids. Normally from such process there results a mixture of the 2-, 3-, and 4-nitro isomers in yields respectively of approximately 62%, 5% and 33%. In distinction to the prior art process, the practice of the present invention provides the 4-nitrotoluene isomer in yields ranging from 56% to 77% and does not necessitate the employment of concentrated nitric acid as required by the prior art.

We have discovered that toluene may be readily and conveniently nitrated to provide such excellent yields of the 4-nitro isomer (or para nitrotoluene) by reacting toluene with cellulose nitrate in the presence of relatively dilute aqueous nitric acid and a mercury catalyst selected from the group consisting of mercury metal, mercurous nitrate, mercuric nitrate and mercuric oxide. Other specified catalyst may be likewise employed. In commercial practice a large proportion of the nitric acid, catalyst and the unreacted cellulose nitrate may be recovered and then recycled into the process. The 4-nitro toluene is then readily separated from the 2- and S-nitro isomers by a freezing process or other standard techniques.

Accordingly a primary object of our invention is to provide a novel method of producing high yields of 4- nitrotoluene.

A more specific object of our invention is to provide a method of producing 4-nitrotoluene in yields ranging from 56% to 77% which comprises nitrating toluene in the presence of cellulose nitrate and aqueous nitric acid in the presence of either mercury or a mercury salt catalyst.

Still another object of our invention is to provide a Bddhd Patented Sept. 15, 1964 that in this case the yields of 4-nitrotoluene are markedly reduced. 7

As the source of cellulose nitrate we used guncotton, i.e., cellulose trinitrate. In most of the experimental results which are hereinafter reported, 10 gram batches of the guncotton were employed.

The present process generally may be readily envisioned by reference to the flow diagram. The first step is to mix toluene with cellulose nitrate and then add either metallic mercury or a mercury salt catalyst, or in some cases Lewis-acid catalysts, along with aqueous nitric acid, in most cases a 50% solution of the latter, after which all of the reactants and catalysts are well mixed. The mixture is then heated in the range of from 20 to '85 C. while being stirred.

We carried out the process at three representative temperatures and varied the times of reaction accordingly. At what is termed low temperature the process was practiced at 25 C. for 20 hours. As an intermediate temperature 60 C. was selected and the reaction was carried out at such temperature for 2 hours. High temperature is one of the order of from to C. and the reaction was carried out for 1 hour at this temperature.

Following the heating, there remains in the reaction vessel both liquid and solid components which are then separated. The solid component may be recovered. Such solid residue comprises nitrocellulose which has not been completely denitrated and can be used for various applications of this material. The liquid portion is separated by standard techniques into aqueous and non-aqeuous aliquots. From the aqueous system the nitric acid and original catalyst may be recovered and recycled in the commercial practice of the invention. The non-aqueous component is washed and neutralized and contains the various mononitrated toluenes and it is from this that the 4-nitrotoluene isomer is separated. This is most readily accomplishedi.e.-separating the 4-isomer from the 2- and 3-isomers by crystallization, i.e., freezing out.

Table 1 presents a nurnber of examples of our process employing different catalysts and various reaction conditions. In carrying out all of these examples, 10 grams of cellulose nitrate was employed. Such cellulose nitrate had a concentration of nitrogen of 13.1% and represents 0.09 mole of the material. 30.3 milliliters of toluene (i.e., 0.28 mole) and 70 milliliters of 50% aqueous nitric acid was used, this representing 0.72 mole. The molar ratio of acid to catalyst was therefore 72 and the acid to nitrocellulose ratio was about 7.2. Further in such table the designation MNT refers to mono-nitrotoluene.

It will be readily apparent to those skilled in this art from the following table of examples that by practicing the present process high yields of 4-nitrotoluene may be readily and conveniently obtained. It is seen from such table, regardless of Whether mercuric nitrate, mercuric oxide, mercurous nitrate or metallic mercury was employed as a catalyst, the proportion of 4-nitrotoluene was more than double that obtainable with the commercial mixed acid process. With the mercuric nitrate catalyst the proportion of the 4-isomer appeared to decrease somewhat as the total yields increased with increasing temperature. In Experiment 21 it is noted that the doubling of the amount of mercuric nitrate resulted in both lower total yield and decreased amount of 4-mononitrotoluene TABLE 1 Efiect of Mercury Catalysts With 50% Nitric Acid n Nitration of Toluene by Nitrocellulose Amount Reaction Yield, total Nitrotoluene conditions MNT Exp. No. Catalyst G. Moles Hrs. T amp, G. Percent Perzcent Percent Perleent 12 3. 2 0. 01 20 RT 4. 3 13 3. 2 0. 01 5 53 5. 9 25 133N092 3. 2 0. 01 2 60 6. 6 5s 32 5 63 18 3. 2 0. 01 1 80 13. 1 106 34 7 59 2.8 0. 01 20 RT 1. 6 13 20 3 77 28 HgNOa 2. 8 0. 01 2 60 5. 5 45 20 3 77 36 2. 8 0. 01 1 80 8. 9 73 28 3 69 16 2. 0 0. 01 20 R I 22 g? 2 $3 75-- 2.0 0. 01 5 78.. Hg (metal) 2. 0 0. 01 2 60 7. 6 01 26 4 70 37.--. 2.0 0. 01 1 80 8. 4 68 25 3 72 44 2. 2 0. 01 20 RT 2. 5 20 G 64 58-. HgO (ycl1ow) 2. 2 0.01 2 60 5.0 26 5 69 65 2. 2 0. 01 1 80 9. 2 75 28 4 68 15 HgClz 2. 7 0. 01 20 RT 0.2 1 3 47 21 Hg(NO )z b 6. 4 0.02 20 RT 1.3 11 31 7 62 s N 20 RT 0.4 3 51 5 44 9 i we 5 53 a. 5 2s 50 e 44 Based on 0.09 M of NC (131% N). b Mole ratios: acid/catalyst=36; acid/NO =7.2.

as compared With its counterpart at 0.01 mole in Experiment 12. Experiment 18 shows the efiects of the nitric acid; in this case the total yield was greater than could be expected and the proportion of the 4-isomer was the lowest obtained. This is further corroborated by Experiments 8 and 9 wherein nitric acid alone was employed, for as is seen the yields here were less than those obtained with a catalyst and the proportion of the 4-isomer fell to 44%. When yellow mercuric oxide was employed as a catalyst the proportion of the 4-isomer tended to remain relatively constant with increasing total mononitrotoluene yields.

to remain relatively constant at a high level, that is, from 70 to 72% of the nitrated toluene reaction products.

That all mercury salts act as a catalyst is disproved by Experiment 15 wherein mercuric chloride was used, as shown in Table 1: it not only caused less than 1% nitration, but further reduced the 4-/2-isomer ratio.

The experiments that are summarized in Table 2 used a mole ratio of acid to catalyst of approximately 72. In Table 2 the amounts of nitrocellulose, toluene and nitric acid were maintained constant but the amount of catalyst was reduced in half to provide a mole ratio of acid to catalyst of approximately 144.

TABLE 2 Efiect of Mercury Catalysts With 50% Nitric Acid on Nitration of Toluene by Nitrocellulose Amount Reaction Yield, total Nitrotolucne conditions MN T a Exp. No. Catalyst G. Moles Hrs. Temp., G. Percent Percent Percent Percent 1'2 3-822 2 2-; s 33 4 a 11.-- 28 6 66 56 g(NOa)2 1. 6 0. 005 2 6.1 40 33 5 62 62. 1. 6 0.005 1 80 8. 3 68 35 6 59 53- 1. 4 0.005 20 RT 2. 2 18 30 4 66 52. HgNO; 1. 4 0.005 2 60 4. 7 38 32 4 62 64- 1. 4 0. 005 l 80 7. 9 64 33 5 62 46 g 885 2g Rg]; 1. 7 14 30 5 65 68 5 5. 1 42 34 3 63 50.-- Hg (metal) 1.0 0.005 2 6O 5. 2 43 35 3 e2 60 1. 0 0. 005 1 80 7.0 57 33 4 62 11 Based on 0.09 M of NC (13.1% N).

Mercurous nitrate gave the highest proportion of the 4-isomer obtained with any of these catalysts at room temperature and at 60 C. while total yields were a little below average for the entire group. At 80 C. the amount of the 4-isomer decreased more than with the other catalysts while the total yield increased. However even with this decrease in the 4-isomer yield the amount was still 69%, about average for the group.

When metallic mercury was employed as the catalyst it is noted that the results are quite interesting. The total yield, starting at 22%, leveled off in the range of from 61 to 68%.

As shown in Table 2, the yields of total monom'trotoluene increased with increasing temperatures and the proportion of the 4-isomer remained relatively constant, although it was not quite as high as yields with the greater amount of catalyst as shown in Table 1.

Table 3 summarizes .a number of experiments carried out with 50% nitric acid solutions in conjunction with metallic mercury or with mercuric and mercurous nitrates at an acid/catalyst molar ratio of approximately 3.6. In all cases the yield of total mononitrotoluene increased with increasing temperatures; however there was a tendency for the amount of 4-isomer to decrease somewhat The amount of 4-isomer, however, tended with increasing total yield.

Efiect of Mercury Catalysts With 50% Nitric Acid on Nitratt'on of Toluene by Nitrocellulose [NC (13.1% N)= g. (0.09 M); toulene=30.3 ml. (0.28 M); HNOs (50%)=35 ml. (0.36 M] [Mole ratios: acid/catalyst=36; acld/NO=3.6]

Amount Reaction Yield, total N itrotoluene conditions MNT Exp. No. Catalyst G. Moles Hrs. T061001) G. Percent Percent Percent Percent 3.2 0.01 RT 1. 5 12 33 6 61 Hg(NOa)2 3. 2 0. 01 2 60 3. 6 32 10 58 3. 2 0.01 1 80 11. 5 94 9 56 2. 8 0. 01 20 RT 2. 2 18 28 7 65 }HgNO 2. 8 0. 01 2 3. 6 29 24 13 63 2. 8 0. 01 1 80 9. 7 79 33 7 60 2.0 0. 01 20 RT 2. 4 19 28 6 Hg (metal) 2. 0 0. 01 2 60 5. 7 4s 30 7 63 2. 0 0. 01 1 80 10. 5 85 36 8 56 Based on 0.09 M of NO (13.1% N).

Table 4 summarizes a number of experiments carried out with 50% nitric acid solutions in conjunction with metallic mercury. or with mercurous and mercuric nitrates' at an .acid/ catalyst molar ratio of approximately trotoluene with 62% of the 4-isorner while the latter gave the same amount of the 4-isorner with only 7% less total mononitrotoluene. When one considers that the price of mercury is normally about one-half that of the salt, it

72 and an :acid to nitrocellulose molar ratio of approxi- 25 may be that the lower total yield will be more desirable mately 3.6. Again in all cases the total mononitrotoluene yield increased with increasing temperature. too, the proportion of the 4-isorner appeared to somewhat decrease as the total yield increased.

Here

TABLE 4 Efiect of Mercury Catalysts With 50% Nitric Acid on Nitration of Toluene by Nitrocellulose [NC (13.1% N) :10 g. (0.09 M) toluene: 30.3 ml. (0.28 M) ;HNOa (50%) :35 ml. (0.36 M)] [Mole ratios acid/catalyst: 72 acid/NC 3.6]

Amount Reaction Yield, total Nitrctoluene conditions MNT Exp. No. Catalyst G. Moles Hrs. T211313. G. Percent Percent Percent Percent 1. 6 0.005 20 RT 1. 3 11 33 8 59 Hg(NO3)2 1. 6 0. 005 2 60 a. 6 29 33 e 61 1. 6 0.005 1 80 6. 6 53 36 7 57 1. 4 0.005 20 RT 1. 1 9 27 6 67 HgNOa 1. 4 0. 005 2 60 6. 5 53 33 7 60 1. 4 0. 005 1 6. 5 53 34 8 58 1.0 0.005 20 RT 1. 7 14 28 G 66 Hg (metal) 1.0 0.005 2 60 4. 7 38 32 8 60 Based on 0.09 M of NO (13.1% N).

From the foregoing table-s it is seen that mercuric nitrate appears to give the best results at concentrations of approximately 0.72 mole of nitric acid. At any particular temperature the yield was greater than that obtained with other acid and catalyst ratios While the proportion of the 4-isomer was the same, it not greater. With mercurous nitrate the situation is essentially the same at reaction temperatures of 60 C. and 80 C. In comparing the different mercury catalysts under the same reaction conditions it appears that there is no positive advantage of one catalyst over another under all reaction conditions. nitrate, appears to give somewhat greater total mononitrotoluene yields in many cases but this is' oftentimes offsolution.

The first catalyst employed, mercuric TABLE 5 from an economic standpoint, under certain conditions.

The effect of 25% nitric acid in conjunction with mercuric nitrate on the nitration of nitrocellulose is given in Table 5. As shown therein, only a very limited reaction took place regardless of the conditions or the amount of catalyst employed. This we deem the lower limit of nitric acid concentration to employ in the present process. Any concentration greater than this can be used with the preferred concentration being a 50% aqueous Efiect of Mercuric Nitrate With 25% Nitric Add on Nltration of Toluene by Nitrocellulose M: 13.1% N) =10 g. (0.09 M); I-INOa (25% =70 ml. 0.32 M) 60 [Toluene=30.3 ml. (0.28M); Hg(NOa)z=1.6 g. (0.005M)] [Mole ratios: acid/catalyst=64; acid/NC =.,.2 (except as noted in table) set by the greater proportion of the 4-isorner obtained EXILNQ Remit) conditions YieldvtotfilMNT with metallic mercury or mercurous nitrate under other 6r particular reaction conditions. For example, Exper-i- 0 2 3 Percent ment 25 with mercuric nitrate gave 58% yield of total mononitrotoluene with 63% of the 4-isomer. Under the 2o Less than 1' same conditions mercurous nitrate in Experiment 28 low- 5 53 Do. ered the total yield to 45% but the amount of the 4- g8 33; isomer was increased to 77%. With metallic mercury D in Experiment 30 the total yield was only 412% but the 6 to amount of 4-isomer Was 73%. One further comparison of mercuric nitrate with metallic mercury as in Experiment 56, the fonrner gave a total yield of 49% mononi- 75 8 Based on 0.09 M of NC (13.1% N).

g. or 0.01 M; acid/eat.=32.

Table 6 summarizes a number of results obtained with various non-mercury catalysts on the nitration of toluene by nitrocellulose. In conjunction with 50% nitric acid certain nitrate salts as therein enumerated were employed. Either because of their proximity to mercury in the Periodic Table of Elements or because of certain similarities and electron arrangements, these salts are identified as cadmium nitrate, zinc nitrate, cuprate nitrate, and plumbous nitrate. Such experiments were conducted at room temperature with approximate acid/catalysts and acid/ 10 nitrocellulose mole ratios of 72 and 7.2 respectively. Although the yields were small, it is indicated that the process of making 4-nitrotoluene may be used with these other catalytic systems.

mate mixture of toluene, nitrocellulose, aqueous nitric acid of a concentration greater than 25% and a catalyst selected from the group consisting of mercury metal, mercurous nitrate, mercuric nitrate, mercuric oxide and mixtures thereof; warming and maintaining said mixture at a temperature ranging from to 85 C. to nitrate said toluene predominantly in the para position and separating the resulting para-nitrotoluene from the other reaction products and from unexpended initial reactants and catalyst.

2. The method of making para-nitrotoluene in substantial yields which comprises the steps of: forming an intimate mixture of toluene, nitrocellulose, aqueous nitric acid in a concentration greater than and a catalyst TABLE 6 Efiect of Various Catalysts on Nitration of Toluene by Nitrocellulose [NC (13.1% N)=10 g. (0.09 M] E Reaction conditions Yield, total MNT u Nitrotoluene xp. No. Reactants Hrs. Tenp G. Percent legcent Pergent Percent 0.72 Ni (70 ml.) HNOa (50%) 48.-. 0.28 M (30.3 ml.) toluene 20 RT 0.5 4 56 8 41 0.10 M Qd(NOs)2.4H2O (3.08 g.) 0.72 M (70 ml.) HNOs (50%) 49." 0.28 M (30.3 ml.) toluene 20 RT 0.5 4 57 3 0.01 M Cu(NO3)2. 3Hz0 (2.41 g.) 0.72 M (70 ml.) HNOQ 51 0.28 M (30.3 ml.) toluene 20 RT 0. 5 4 58 3 39 0.01 M Zn(NOa)r. 3H2O (2.50 0.72 M (70 ml.) HNOa (50%) 0.28 M (30.3 ml.) toluene 20 RT 0. 2 1 42 6 52 70 lg.gg5l\ld(lb(lil)) l. 311 0 (1.65 g 91m. ouene 10.01 M B11 moan (in toluene) 1 42 g) i 20 RT 9 41 2 57 72--- {0.84 M (91 m1.) toluene 1 80 2 4 20 2 54 0.1 M BF3. O(C2H5)z (in toluene) (1.42 g.) 44

' Based on 0.9 M of NO (13.1 N).

In addition to this, several experiments were conducted with boron trifluoride-etherate alone as the catalysts. Although the total yields were low, the proportion of the 4- isomer was in the range of from 55% to In carrying out the above experimental procedures, as briefly noted in the introduction to the specification and in the attached flow diagram, the nitrocellulose was mixed with toluene in a reaction flask and the other reagents were then added. At the end of the reaction period the reaction mixture was cooled, diluted with excess water and filtered. In certain cases it was necessary to centrifuge the solid reaction product. The precipitate was washed with ether and ligroin (3060), the filtrates combined, washed with /z-saturated sodium bicarbonate solution and finally washed with copious quantities of water. The organic phase was separated, dried by conventional methods and the volatile solids were removed with a rotating evaporator under reduced pressure obtained with aspirator. The residue was weighed and analyzed for isomers of nitrotoluene.

It should be noted that excess water is somewhat deleterious to the present process and is removed from the reactants by conventional techniques.

In view of the above specification it will be obvious that various modifications and variations may be effected without departing from the spirit and the scope of the novel concepts of our invention.

We claim as our invention:

1. The method of making para-nitrotoluene in substantial yields which comprises the steps of: forming an intiselected from the group consisting of mercury metal, mercurous nitrate, mercuric nitrate, mercuric oxide and mixtures thereof; warming and maintaining said mixture at a temperature ranging from 20 to C. for a period of from 1 to 24 hours; separating the solid from the liquid components of the reaction mass; separating said liquid component into an aqueous and non-aqueous fraction; washing and neutralizing said non-aqueous fraction and separating the para-nitrotoluene contained therein from the other reaction products.

3. The method of making para-nitrotoluene which comprises the steps of: forming an intimate mixture of toluene, nitrocellulose aqueous nitric acid in a concentration ranging from 25% to 50% and a catalyst selected from the group consisting of mercury metal, mercurous nitrate, mercuric nitrate, mercuric oxide and mixtures thereof; warming and maintaining said mixture at a temperature ranging from 20 to 85 C. to nitrate said toluene in the para position and separating the resulting para-nitrotolucue from the other reaction products and from unexpended initial reactants and catalyst.

4. The method of making para-nitrotoluene in good yields which comprises the steps of: forming an intimate mixture of toluene, nitrocellulose, aqueous nitric acid in a concentration greater than 25 and a catalyst consisting of boron trifiuoride in ether; warming and maintaining said mixture at a temperature ranging from 20 to 85 C. to nitrate said toluene, and separating the resulting paranitrotoluene from the other reaction products and from unexpended initial reactants and catalyst.

9 10 5. The method of making mono-nitrotoluene which References Cited in the file of this patent comprises the steps of: forming an intimate mixture of FOREIGN PATENTS toluene, nitrocellulose, aqueous nitric acid in a concentration greater than 25% and a catalyst selected from the 333x708 Germany 1921 group consisting of mercury metal, mercurous nitrate, 5 OTHER REFERENCES mercuric nitrate, mercuric oxide and mixtures thereof; warming and maintaining said mixture at a temperature ranging from 20 to 85 C. to nitrate said toluene and separating the resulting mono-nitrotoluene from unexpended initial reactants, catalyst, and partially denitrated 10 nitrocellulose.

Topchiev: Nitration of Hydrocarbons and Other Organic Compounds (1959), pub. by Pergamon Press, New York, pages 43-61. 

1. THE METHOD OF MAKING PARA-NITROTOLUENE IN SUBSTANTIAL YIELDS WHICH COMPRISES THE STEPS OF FORMING AN INTIMATE MIXTURE OF TOLUENE, NITROCELLULOSE, AQUEOUS NITRIC ACID OF A CONCENTRATION GREATER THAN 25% AND A CATALYST SELECTED FROM THE GROUP CONSISTING OF MERCURY METL, MERCUROUS NITRATE, MERCURIC NITRATE, MERCURIC OXIDE AND MIXTURES THEREOF; WARMING AND MAINTAINING SAID MIXTURE AT A TEMPERATURE RANGING FROM 20* TO 85*C. TO NITRATE SAID TOLUENCE PREDOMINANTLY IN THE PARA POSITION AND SEPARATING THE RESULTING PARA-NITROTOLUENE FROM THE OTHER REACTION PRODUCTS AND FROM UNEXPENDED INITIAL REACTANTS AND CATALYST. 